Levulinic acid (“LA”) can be used to make resins, plasticizers, specialty chemicals, herbicides and as a flavor substance. Levulinic acid is useful as a solvent, and as a starting material in the preparation of a variety of industrial and pharmaceutical compounds such as diphenolic acid (useful as a component of protective and decorative finishes), calcium levulinate (a form of calcium for intravenous injection used for calcium replenishment and for treating hypocalcemia. The use of the sodium salt of levulinic acid as a replacement for ethylene glycols as an antifreeze has also been proposed.
Esters of levulinic acid are known to be useful as plasticizers and solvents, and have been suggested as fuel additives. Acid catalyzed dehydration of levulinic acid yields alpha-angelica lactone.
Levulinic acid has been synthesized by a variety of chemical methods. But levulinic acid has not attained much commercial significance due in part to the high cost of the raw materials needed for synthesis. Another reason is the low yields of levulinic acid obtained from most synthetic methods. Yet, another reason is the formation of a formic acid byproduct during synthesis and its separation from the levulinic acid. Therefore, the production of levulinic acid has had high associated equipment costs. Despite the inherent problems in the production of levulinic acid, however, the reactive nature of levulinic acid makes it an ideal intermediate leading to the production of numerous useful derivatives.
Cellulose-based biomass, which is an inexpensive feedstock, can be used as a raw material for making levulinic acid. The supply of sugars from cellulose-containing plant biomass is immense and replenishable. Most plants contain cellulose in their cell walls. For example, cotton comprises 90% cellulose. Furthermore, it has been estimated that roughly 75% of the approximate 24 million tons of biomass generated on cultivated lands and grasslands are waste. The cellulose derived from plant biomass can be a suitable source of sugars to be used in the process of obtaining levulinic acid. Thus, the conversion of such waste material into a useful chemical, such as levulinic acid, is desirable.
In the synthesis of levulinic acid (LA) from carbohydrates, the reactions are typically performed in the presence of water and strong mineral acids, like sulfuric acid (SA). After the levulinic acid is synthesized, it has to be efficiently and selectively removed from the aqueous mineral acid mixture. Perhaps one of the most practical methods utilizes liquid liquid extraction to extract the LA into an organic solvent. Liquid-liquid extraction is efficient for extracting levulinic acid, but it is not completely selective with regards to extracting levulinic acid and not extracting sulfuric acid. Thus, sulfuric acid is extracted into the organic extraction solvent with the levulinic acid. Sulfuric acid can be problematic during subsequent purification steps because it can help catalyze side reactions of levulinic acid and the extraction solvent.
After extraction of LA from the solvent, the solvent must be purified by distillation at moderate to high temperatures and then, optionally, recycled back into the process in order for the process to be practical economically. However, if sulfuric acid is not removed appreciably from the organic extraction solvent containing LA, then there are considerable yield losses of the extraction solvent and LA due to side reactions that can be catalyzed by mineral acid.
Thus, a need exists for a method to remove sulfuric acid or minimize the amount of sulfuric acid present in the organic extraction solvent and LA in order to prevent or minimize side reactions of the organic extraction solvent and LA.